1. Field of the Invention
The present invention relates to a motor that can be constructed in microstructure with enhanced workability.
2. Related Background Art
Among conventional compact motors, there is, for example, a compact, cylindrical step motor as shown in FIG. 13. A stator coil 105 is concentrically wound on each of bobbins 101, and each bobbin 101 is fixed as being axially sandwiched between two stator yokes 106. The stator yoke 106 have stator teeth 106a and stator teeth 106b arranged in alternating fashion along the circumferential direction of the bore surface of bobbin 101. The stator yokes 106 integral with the stator teeth 106a or 106b are fixed to cases 103, thus composing stators 102.
Flange 115 and bearing 108 are fixed to one of two sets of cases 103 and another bearing 108 is fixed to the other case 103. Rotor 109 is comprised of a rotor magnet 111 fixed to rotor shaft 110, and the rotor magnet 111 and the stator yoke 106 of stator 102 form radial gap portions. The rotor shaft 110 is rotatably supported between the two bearings 108.
The conventional compact step motor described above, however, had the drawback that the outside dimensions of motor were large, because the cases 103, bobbins 101, stator coils 105, stator yokes 106, etc. were concentrically located outside the rotor. In addition, it has another drawback that the output of motor is not high, because the magnetic flux generated by energizing the stator coils 105 mainly passes end faces 106a1 of the stator teeth 106a and end faces 106b1 of the stator teeth 106b, as shown in FIG. 14, and does not effectively act on the rotor magnet 111.
The applicant proposed a motor solving such problems in U.S. patent application Ser. No. 08/831,863 (filed Apr. 2, 1997).
This proposed motor is constructed in such structure that the rotor of permanent magnet partitioned and magnetized in the alternately different poles at equal intervals in the circumferential direction is formed in a cylindrical shape, that a first coil, the rotor, and a second coil are located in order along the axial direction of the rotor, that the first outside pole and first inside pole excited by the first coil are opposed to outside and inside peripheral surfaces of the rotor, and that the second outside pole and second inside pole excited by the second coil are opposed to the outside and inside peripheral surfaces of the rotor.
The motor of this structure was able to provide high output and had small outside dimensions of motor, but the radial dimension of the first inside pole and second inside pole which comprise a pair of magnetic tooth with separated tip ends was also small. When these pole teeth were processed by press working, there were problems of strength of mold, emission of chip, and so on. Therefore, the processing was not easy and it was rather difficult to achieve high strength of the teeth. There were desires for readily processing the first outside pole and second outside pole, too.